1. Field of the Invention
The present invention relates to a controller area network (CAN) system that controls send/receive among a plurality of electric control units located within a vehicle and the like. In particular, the invention relates to a CAN system that facilitates evaluation of communication quality.
2. Description of the Background Art
In the recent years, a variety of electric control units (ECUs) are located within vehicles and medical equipments. The send/receive of information between the units is controlled by a CAN system that is one of local area networks (LANs).
It should be the first priority to secure operational safety in the vehicles and medical equipments. Therefore the CAN system focuses on correcting of errors and protection against occurrence of errors, and it is paramount important to secure communication quality between the units.
For example, Japanese Patent Application Publication Laid-Open Nos. 2003-244779 and 2003-229875 disclose art in relation to this application.
There are the following problems in conventional CAN systems in time of evaluating communication quality.
Specifically, in evaluation of communication quality as to whether individual ECUs within a CAN system can recognize error data, it is necessary to purposely generate error data on a communication bus within the CAN system. The occurrence of this error data can be achieved by connecting, to the communication bus, hardware that can generate reproducible interference on the communication bus. Specific examples of such hardware are Vector-manufactured “CANstressD” and “CANstressDR.”
However, the communication quality evaluation using such hardware may fail to accurately generate error data at an assumed position in a communication signal. For example, although ISO11898 (so-called CAN-class C) specifies communication rates from 125 kbps (kilo-bit per second) to 1 Mbps (mega-bit per second), the above-mentioned hardware complies with only communication rates of up to 125 kbps in order to prevent delays in the insert timing of error data, and it does not comply with the highest communication rate of 1 Mbps. It is therefore impossible for the communication quality evaluation using the above hardware to perform accurate error data generation and communication quality evaluation in case of operations at a communication rate of 1 Mbps.
There is also a problem in starting a self-diagnostic program.
For a vehicle employing a CAN system, in general, a fixed storage unit within a microcomputer is often equipped with a self-diagnostic program. This is for the purpose of detecting any abnormal operation in the event that, due to prolonged use, a vehicle-borne semiconductor device deteriorates to cause a poor operation.
A self-diagnostic program generally employs a loop back mode that receives sent communication data for itself. Since the loop back mode assumes communication in which send/receive is carried out normally, it is possible to check circuit defects in normal communication. However, the loop back mode does not assume communication containing error data, and it is therefore impossible to evaluate communication containing error data. Hence, it is impossible to check whether a circuit for error detection processing (i.e., error management circuit) itself has a defect.